The purpose of this work was to determine the frequency of infection by fungal endophytes in Festuca rubra plants from Mediterranean permanent grasslands (dehesas). Plants infected with the fungal endophyte Epichloë festucae were detected in all twenty‐seven populations studied in the province of Salamanca, Spain. Infection frequencies in six selected populations ranged from 44% to 92% (average, 70%) of the plants. Infected plants were almost always symptomless. These results suggest that the association between E. festucae and F. rubra is common and occurs at a high frequency in Mediterranean permanent grasslands.